The invention relates to a filtering apparatus, comprising an inlet channel for the flow to be filtered, an outlet channel for the filtered flow, a number of parallel filtering elements open from both ends, into which the flow to be filtered may be directed so that the infiltration occurs out of the element through the element jacket, and at least one washing organ connecting alternately to the ends of different elements at both ends of the filtering elements, forming an outlet channel for the backflushing of elements generated with the pressure of the filtered flow.
A filtering device is needed especially in motors as a fuel or luboil filter, with the continuous backflushing of which the operation of the motor is ensured in long-term continuous use. The apparatus typically comprises a large number of filtering elements, which are continuously in operation except for the washing period running in a few elements at a time.
A state-of-the art backflushable filtering apparatus has been described in the patent publication DE-4 340 275. The apparatus comprises parallel, candle-shaped filtering elements arranged around a vertical axle as two nested rings. The flow to be filtered is directed into the elements from their upper and lower ends, and the infiltration occurs out of the element through the cylindrical jacket of each element. For backwashing the elements, two washing arms of different lengths are arranged below them, the arms being fastened to the rotatable vertical axle of the apparatus. The rotating motion of the axle and the washing arms is achieved with the help of a turbine rotor arranged in the flow inlet channel and cogwheels connected to the rotor and acting as transmission mechanism. The movement of the washing arms is thus maintained by utilising the motion energy of the flow coming into the apparatus. The washing arms are arranged to alternately connect to the lower ends of different filtering elements so that they form outlet channels for the washing flow. Corresponding to the elements, closers are attached to the rotatable axle of the apparatus above the filtering elements, the closers shutting the upper end of the filtering element in question during the washing stage, thus preventing the flow to be filtered from mixing with the washing flow.
The drawback of the backflushing arranged according to the publication DE-4 340 275 is in practice that the filtering elements are cleaned well only from their lower ends, in which the washing suction has the strongest effect. The situation is made worse by the fact that the flow is channelled to a place in which the flow resistance is the smallest, i.e. the washing arms absorb liquid from the lower ends of the elements being cleaned or already cleaned at the same time as the upper ends of the elements remain more or less without washing.
One has tried to solve the said problem by leaving a small opening to the upper end of the filtering element to be washed for the flow-through of washing liquid. In other words, the intention is to complete backflushing with a washing flow sweeping the inner surface of the element jacket. However, as the countercurrent flow penetrating the element jacket is substantially more effective in releasing the precipitate gathered into the jacket than the flow-through inside the jacket, and as the flow-through may in its part deter the countercurrent flow penetrating the jacket, the improvement achieved with the solution remains imperfect.
The patent publication U.S. Pat. No. 3,318,452 discloses a filtering apparatus, in which washing arms are arranged to the opposite ends of the filtering candles, the arms linking simultaneously to the ends of the candles. This makes the backflushing more effective in the vicinity of the candle ends, but in the middle part of the candle the suctions directed to opposite directions annul each other so that washing is weaker in this part of the candle.
The object of the invention is to remove the drawbacks in the state-of-the-art technology and to provide a filtering apparatus, in which the backflushing of filtering elements may be carried out in a more effective way than before. It is characteristic of the filtering apparatus of the invention that each of the filtering elements is divided into two parts between the ends so that the washing organ connected to the end of the element creates backflushing only to a part of the element length at a time.
In the filtering element of the invention, each filtering element can be washed with a washing suction directed to its both ends so that the element parts experience identical washing, and the cleaning effect of the washing directed to the element jacket becomes substantially more effective. With this arrangement, the problem of the filtering apparatus of the publication DE-4 340 275, i.e. that the other end of the filtering element continuously suffers poor washing, is avoided.
By dividing the filtering element in two in accordance with the invention, it is especially achieved that the washing is directed only to a part of the whole jacket surface of the element, which means more effective washing. A further advantage is that the element parts can now be flushed independently irrespective of each other, and it is not necessary to separately close the opposite end of the element when washing the other part of the element. On the contrary, the filtering may continue in the one part of the element as the other part is washed, which increases the capacity of the apparatus.
Connecting the filtering element to the washing suction alternately from its different ends may also generate an impulse directed to the element, assisting in releasing the cake of solid matter collected to the element jacket and thus in cleaning the element.
The said division of the filtering element in two may be carried out substantially by a solid partition arranged to the middle of the element. The element is then divided into two parts, which are operationally independent from each other. Alternatively, the interior of the filtering element may be constricted from between the ends so that there is a narrow flow opening in the constriction point, letting the washing flow-through to the element part which is to be backflushed. For example, it is possible to provide the element with a partition, to which an inclined or curved flow opening is formed so that it generates a spiral flow-through into the element part to be washed. This kind of arrangement has a substantially bigger cleaning effect to the inner surface of the element than a direct linear flow-through.
In the filtering apparatus of the invention, the washing elements at the opposite ends of the filtering elements may advantageously be connected to each other as one piece rotating around the axle of the apparatus. No additional mechanisms for generating the rotating movement of the different washing elements are thus needed.
The washing elements may be tubular washing arms transverse to the direction of the filtering elements. The filtering elements may be arranged as one or several rings around the rotation axle of the washing arms. Respectively, one or several washing arms are needed at both ends of the elements, the length of the arms corresponding to the radii of the said rings. Upon rotating, each washing arm connects alternately to the ends of different elements for generating the backflushing of the elements.
The common rotation axle for the washing organs of the different ends of the said filtering elements is preferably provided with a channel, through which all the washing elements are in connection with the same discharge assembly. The said axis, as well as the washing organs, may consist of hollow tubes, along which the washing flow is discharged. The discharge assemblies may be in the ambient pressure so that the washing works with the pressure difference between the pressure of the filtered flow surrounding the filtering elements and the ambient pressure.
The washing organs at the opposite ends of the filtering elements may be arranged opposite each other so that they connect simultaneously to each filtering element, thus generating the washing of the element with the washing suction simultaneously from both ends. However, it is as well possible to arrange the washing organs to connect to different ends of each of the filtering elements at different stages.